A large number of locking devices have been presented for securing doors of homes, apartments and the like, each of which has a movable member which can be selectively placed with one end imbedded in the door and one end extending into the jamb. A major deficiency of these devices is that they are prone to both picking and to having the end forced out of the jamb.
Another approach has been to use a series of locks for a single door including, in some cases, what is known in the industry as a dead bolt. The difficulty with this latter approach is that it achieves higher security at the price of costly and complex locking systems, together with significantly increasing the amount of time and effort which must be expended to lock and unlock the door.
A related problem involves permitting the door to be partially opened in order to, for example, receive a small package while simultaneously reserving some security. Here, a number of chains have been presented for selectably coupling the door to the door jamb. These devices however are ordinarily held in place by relatively small screws, especially where the door is of hollow, lightweight construction, and are displaceable by subjecting a modicum of force against the door.